The overarching objective of this proposal is to attain data for FDA 510(k) submission of a handheld miniaturized STAT Blood Counter using 5-10 L blood to yield a complete blood count (CBC) with 3-part differential. This dramatically decreased size and sample volume creates new opportunities in delivery of these hematology tests, ultimately leading to more streamlined, available, and on demand care. In Phase I, we showed proof-of-concept for our microfluidic approach for blood dilution, developed a miniature flow cytometry module, and demonstrated impedance measurements of blood. In Phase II, we developed a microvolume sample consumable, demonstrated blood dilution in our spiral vortexer micromixer, brought our miniature optical block's performance up to par with larger cytometers, and developed a concept model of our blood sensor. Here in this Phase IIB, we plan to fully engineer a product version of our STAT Blood Counter and validate it at Boston Children's Hospital. We are proposing that most of the product development will occur in Years 1-2 and the validation and submission in Year 3. At the conclusion of the effort, we will have submitted our technology for FDA 510(k) approval for CBC with 3-part differential. This will enable capabilities for measuring blood loss, infection, and bleeding risk in a range of different settings including the clinic, emergency rooms, ambulances, developing countries, and the field.